This invention relates to the production of perfluorocarboxylic acids by means of a metathesis reaction between a perfluorocarboxylic acid fluoride and an alkanoic acid.
Perfluorocarboxylic acids are items of commerce which have a broad scope of utility. For example, perfluorooctanoic acid can be used as a reagent to provide fluorine-containing groups on a polymer molecule thus imparting water-repellency and soil-resistance to fibers and fabrics prepared from such a modified polymer. Similarly, trifluoroacetic acid can be used as a catalyst and is a chemical intermediate in the production of pharmaceutical, agricultural, and industrial products.
The production of perfluorocarboxylic acids utilizing electrochemical techniques is known and recent developments in the field of electrochemical fluorination chemistry have made such techniques even more attractive. However, the primary cell products of such electrochemical fluorination techniques are invariably in the form of the acid fluorides, e.g., trifluoroacetyl fluoride. Thus, in order to obtain the desired perfluorocarboxylic acid, e.g., trifluoracetic acid, this primary cell product must be converted to the free acid. This can be done by a metathesis reaction between the perfluoroacid fluoride and a carboxylic acid. The electrochemical process and the metathesis reaction, however, result in the formation of undesirable contaminants and by-products such as HF, H.sub.2 O and/or carbonyl fluoride.
As mentioned above, electrochemical fluorination is a convenient process for producing the perfluoroacyl fluoride starting materials for the metathesis reaction. Though electrochemical fluorination is an efficient process, its perfluoroacyl fluoride cell product contains minor amounts of by-products such as carbonyl fluoride and hydrogen fluoride. Such materials are difficultly removable from the primary product because of similar boiling points, a tendency to form complexes, or other reasons. In addition, there are always opportunities for the introduction of small amounts of extraneous water into the system. The presence of minor amounts of materials such as hydrogen fluoride, carbonyl fluoride, or water has been found to hinder the above-described metathesis reaction and/or to complicate the isolation and/or recovery of the desired metathesis product.